Presynaptic inhibition (PSI) has been shown to modulate several neuronal pathways of functional relevance by selectively gating the connections between sensory inputs and spinal motoneurons, thereby regulating the contribution of the stretch reflex circuitry to the ongoing motor activity. In this study, we investigated whether a differential regulation of Ia afferent inflow by PSI may be associated with the performance of two types of plantarflexion sensoriomotor tasks. The subjects (in a seated position) controlled either: 1) the force level exerted by the foot against a rigid restraint (force task, FT); or 2) the angular position of the ankle when sustaining inertial loads (position task, PT) that required the same level of muscle activation observed in FT. Subjects were instructed to maintain their force/position at target levels set at ~10% of maximum isometric voluntary contraction for FT and 90° for PT, while visual feedback of the corresponding force/position signals were provided. Unconditioned H-reflexes (i.e. control reflexes) and H-reflexes conditioned by electrical pulses applied to the common peroneal nerve with conditioning-to-test intervals of 21 ms and 100 ms (corresponding to D1 and D2 inhibitions, respectively) were evoked in a random fashion. A significant main effect for the type of the motor task (FT vs PT) (p = 0.005, η2 p = 0.603) indicated that PTs were undertaken with lower levels of Ia PSI converging onto the soleus motoneuron pool. Additionally, a significant interaction between the type of inhibition (D1 vs D2) and the type of motor task (FT vs PT) (p = 0.038, η2 p = 0.395) indicated that D1 inhibition was associated with a significant reduction in PSI levels from TF to TP (p = 0.001, η2 p = 0.731), whereas no significant difference between the tasks was observed for D2 inhibition (p = 0.078, η2 p = 0.305). These results suggest that D1 and D2 inhibitions of the soleus H-reflex are differentially modulated during the performance of plantarflexion FT and PT. The reduced level of ongoing PSI during PT suggests that, in comparison to FT, there is a larger reliance on inputs from muscle spindles primary afferents when the neuromuscular system is required to maintain position-controlled plantarflexion contractions.
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机译：突触前抑制（PSI）已显示可通过选择性地控制感觉输入和脊髓运动神经元之间的连接来调节功能相关的几种神经通路，从而调节拉伸反射电路对正在进行的运动活动的作用。在这项研究中，我们调查了PSI对Ia传入流入的差异调节是否可能与两种类型的plant屈感觉运动任务的执行有关。受试者（坐在座位上）控制以下任一情况：1）脚在刚性约束下施加的力水平（力任务，FT）；或2）承受惯性载荷（定位任务，PT）时踝关节的角位置，惯性载荷需要在FT中观察到相同水平的肌肉激活。指示受试者将力/位置保持在目标水平，目标水平设置为FT的最大等距自动收缩的10％，PT的最大角度为90°，同时提供相应力/位置信号的视觉反馈。分别在21毫秒和100毫秒的调节至测试间隔（分别对应于D1和D2抑制）中诱发无条件的H反射（即对照反射）和由施加到腓总神经的电脉冲调节的H反射。随意的时尚。对于运动任务类型（FT vs PT）的显着主要影响（p = 0.005，η 2 p = 0.603）表明，进行PT时Ia PSI的水平较低，并收敛到比目鱼运动神经元上池。此外，抑制类型（D1 vs D2）和运动任务类型（FT vs PT）之间存在显着的相互作用（p = 0.038，η 2 p = 0.395），表明与D1抑制相关从TF到TP的PSI水平显着降低（p = 0.001，η 2 p = 0.731），而对于D2抑制，任务之间没有显着差异（p = 0.078，η 2 p = 0.305）。这些结果表明，在进行足底屈曲FT和PT的过程中，比目鱼H-反射的D1和D2抑制作用被不同地调节。与FT相比，PT期间PSI持续水平的降低表明，当需要神经肌肉系统维持位置控制的足底屈曲收缩时，对肌肉纺锤初次传入的输入的依赖性更大。
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